This invention relates to a method and apparatus for forming a cavity in soft tissue or bone in a minimally invasive manner. More particularly, it relates to a rotary cutting bit that may be inserted percutaneously, such as through a needle or cannula, and then expanded in diameter upon rotation to form an internal cavity having a radius many times that of the insertion opening, and to structure and steps for controlling the location of one or both of the ends of the cavity that is being formed.
The Background of the Invention in my U.S. Pat. No. 5,928,239, granted Jul. 27, 1999, and entitled Percutaneous Surgical Cavitation Device And Method is hereby made a part of this Background of the Invention.
My U.S. Pat. No. 5,928,239 discloses a rotating cutting tool for forming a cavity inside a body region. The cutting tool is inserted through a small diameter access opening into the body region where the cavity is to be formed. The cutting tool is moved forwardly to where the forward end boundary of the cavity is to be formed. Then, the cutting bit is rotated and is sometimes pulled rearwardly to lengthen the cavity. Eventually, a rearward end boundary is formed.
As explained in my U.S. Pat. No. 5,928,239, more than one cutting tip member can be used for forming a given cavity. For example, a first cutting tip member of a predetermined length can be used for cutting a substantially semi-cylindrical first end portion of the cavity. Then, a second cutting bit having a shorter cutting tip member may be substituted for the first cutting bit and then rotated for cutting a central portion of the cavity that is smaller in diameter than the first end portion. Then, the second cutting bit can be replaced by the first cutting bit and the first cutting bit can be used to form a substantially semi-spherical second end portion for the cavity. Or, as also disclosed in my U.S. Pat. No. 5,928,239, a single size cutting bit can be used to form the entire cavity. In either case, cutting is started at a first end boundary of the cavity and is continued on to a second, opposite end boundary of the cavity. Rotation is started with the cutting tip member positioned to cut the first end boundary. Then, the cutting bit may be moved axially while it is being rotated so as to lengthen the cavity. The endwise movement of the cutting tool is continued until the cutting tip member is positioned at the second, opposite end boundary of the cavity.
There is a need for an apparatus and method for accurately establishing one or both end boundaries of the cavity and for preventing unwanted cutting beyond the boundary or boundaries. It is an object of the present invention to provide such an apparatus and method.
According to the present invention, a cavity cutting bit is provided that has an elongated shaft that includes a forward end, a cutting tip member that includes a cutting end and a mounting end, and a hinge that pivotally connects the mounting end of the cutting tip member to the forward end of the shaft. The cutting tip member is mounted on the forward end of the shaft for free swinging relative to the shaft between a position in which the cutting tip member is coaxial with the shaft and a position in which the cutting tip member extends at an angle from the shaft. The cutting bit is inserted, cutting tip member first, into a small diameter opening or passageway that leads into the interior of a body part. At this time, the cutting tip member is coaxial with the elongated shaft. When properly located within the body part, the cutting bit is rotated. In response to this rotation, the cutting tip member swings outwardly and acquires a cutting or fly diameter that is substantially larger than the small opening through which it and the shaft were inserted.
According to an aspect of the invention, the apparatus is provided with a cutting bit guide member having a forward end portion that is adapted to be placed against an outer surface region of a body part and a guide passageway that is adapted to receive the cutting tip member and the shaft, in that order. An abutment is provided on the shaft at a predetermined distance rearwardly from the cutting tip member. The apparatus includes an axial movement stop for the shaft having a stop surface that is at a predetermined fixed position relative to both the forward end portion of the guide member and the abutment on the shaft. In use, the forward end portion of the guide member is placed against the outer surface region of the body part. Then the cutting tip member and the shaft are inserted into the guide passageway and are moved into the body part to where a cavity is to be formed. The shaft is allowed to be moved endwise until the abutment on it is against the stop surface. The shaft is rotated to cause the cutting tip member to swing outwardly and form the cavity. Movement of the abutment against the stop surface prevents further endwise movement of the cutting tip member and establishes a predetermined first end boundary for the cavity.
According to another aspect of the invention, the guide member is adjustable in length for changing the distance between the forward end surface of the guide member and the stop surface.
According to a further aspect of the invention, the apparatus is provided with two axial movement stops, each having a stop surface that confronts the other stop surface. The abutment on the shaft is located between the two stop surfaces. Movement of the abutment against one of the stop surfaces establishes a first end boundary for the cavity that is formed during rotation of the cutting bit. Movement of the abutment against the other stop surface establishes a second, opposite end boundary for the cavity.
According to yet another aspect of the invention, either one or both of the movement stops is adjustable in position relative to the other movement stop, for changing the distance between the two stop surfaces and for changing the positions of the two stop surfaces relative to the forward end surface of the guide member.
In the preferred embodiment, the first motion stop extends upwardly from and substantially perpendicular to an elongated base member and the guide member extends forwardly from the first motion stop. Preferably also, the guide member is adjustable in length for adjusting the position of its forward end surface relative to the stop surface on the motion stop member.
A method aspect of the invention includes the step of providing a percutaneous access opening into a body part in which a cavity is to be formed. Providing a stop member spaced outwardly from the access opening and providing said stop member with a shaft receiving opening. Inserting through the shaft opening and then through the access opening a rotary cavitation device comprising (i) an elongated shaft having a radius and an axis of rotation, (ii) a cutting tip member having a fixed length; (iii) a hinge interconnecting the shaft and the cutting tip member and allowing a free swinging movement of the cutting tip member between a position in which the cutting tip member is coaxial with the shaft and a second position in which the cutting tip member extends outwardly at an angle from the shaft; and (iv) an abutment on the shaft rearwardly of the stop member. The shaft abutment and the stop member are positioned such that when the shaft is moved axially forwardly to place the abutment into contact with the stop member, the cutting tip member is positioned at an end boundary of the internal cavity that is to be formed in the body part. Then, the shaft is rotated at a velocity sufficient to cause the cutting tip member to swing from its first position into its second position. The cutting tip member is moved as necessary to form the desired internal cavity in the body part and provide such cavity with a radius that is greater than the radius of the shaft. Thereafter, the shaft and the cutting tip member are withdrawn from the access opening.
A further aspect of the invention involves providing a second stop member that is spaced outwardly from the abutment on the shaft. This positions the abutment between the two stop members. The second stop member is positioned at such a location that when the shaft is retracted to move the abutment into contact with the second stop member, the cutting tip member is at a second, opposite end boundary of the cavity that is being formed.
In preferred form, the forward stop member is provided with a forwardly projecting guide tube having a front end surface that is positionable against a surface portion of the body part that is outwardly of where the cavity is to be formed. The guide tube is provided with a passageway for the rotary cavitation device that is in alignment with the shaft receiving opening in the stop member. The cutting tip member of the rotary cavitation device is inserted forwardly into and through the guide passageway and into and through the access opening into the body part and is then rotated to form the cavity.
According to yet another aspect of the invention, the shaft abutment and the stop member can be positioned by adjusting the length of the guide tube.
The second stop member may be mounted on a longitudinal base member that includes lead screw thread. This base member is positioned on a longitudinal frame member that is connected to the first stop member. An adjustment ring is provided that surrounds the base member and the frame member and includes internal threads that engage the lead screw threads on the base member. The ring is rotated for causing movement of the base member and the second stop member relatively along the frame member for purposes of positioning the second stop member.
Other objects, advantages and features of the invention will become apparent from the description of the best mode set forth below, from the drawings, from the claims and from the principles that are embodied in the specific structures that are illustrated and described.